[Mlir-commits] [mlir] [mlir][vector] Guard transfer read narrow type emulation (PR #208873)

[llvmlistbot at llvm.org]

https://github.com/qyingwu updated https://github.com/llvm/llvm-project/pull/208873

>From 7bc50a3c052d3253af97bafec16793036a02d305 Mon Sep 17 00:00:00 2001
From: qyingwu <qiyingwu at utexas.edu>
Date: Fri, 10 Jul 2026 20:42:06 -0700
Subject: [PATCH] [mlir][vector] Guard transfer read narrow type emulation

---
 .../Vector/Transforms/VectorEmulateNarrowType.cpp  | 14 +++++++++++++-
 .../Vector/vector-emulate-narrow-type-invalid.mlir | 10 ++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 mlir/test/Dialect/Vector/vector-emulate-narrow-type-invalid.mlir

diff --git a/mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp b/mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp
index 9faaebdcf8f35..2286dd1cb995d 100644
--- a/mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp
+++ b/mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp
@@ -51,6 +51,13 @@ using MemRefValue = TypedValue<MemRefType>;
 // Utils
 //===----------------------------------------------------------------------===//
 
+/// Returns true for element widths supported by this sub-byte emulation. This
+/// is intentionally width-only: both integer and float element types with these
+/// widths are handled by existing patterns.
+static bool isSupportedSubByteElementWidth(unsigned bitWidth) {
+  return bitWidth == 2 || bitWidth == 4;
+}
+
 /// Returns a compressed mask for the emulated vector. For example, when
 /// emulating an eight-element `i8` vector with `i32` (i.e. when the source
 /// elements span two dest elements), this method compresses `vector<8xi1>`
@@ -1307,6 +1314,11 @@ struct ConvertVectorTransferRead final
         cast<MemRefType>(adaptor.getBase().getType()).getElementType();
     Type emulatedElemTy = op.getType().getElementType();
     int emulatedBits = emulatedElemTy.getIntOrFloatBitWidth();
+    if (!isSupportedSubByteElementWidth(emulatedBits))
+      return rewriter.notifyMatchFailure(
+          op, "only 2-bit and 4-bit sub-byte type is supported at this "
+              "moment");
+
     int containerBits = containerElemTy.getIntOrFloatBitWidth();
 
     // Check per-element alignment.
@@ -1683,7 +1695,7 @@ static LogicalResult alignedConversionPrecondition(PatternRewriter &rewriter,
   assert(containerBits % 8 == 0 && "Not a multi-byte scalar type!");
 
   // TODO: Add support other widths (when/if needed)
-  if (subByteBits != 2 && subByteBits != 4)
+  if (!isSupportedSubByteElementWidth(subByteBits))
     return rewriter.notifyMatchFailure(
         op, "only 2-bit and 4-bit sub-byte type is supported at this moment");
 
diff --git a/mlir/test/Dialect/Vector/vector-emulate-narrow-type-invalid.mlir b/mlir/test/Dialect/Vector/vector-emulate-narrow-type-invalid.mlir
new file mode 100644
index 0000000000000..4b092331ce3df
--- /dev/null
+++ b/mlir/test/Dialect/Vector/vector-emulate-narrow-type-invalid.mlir
@@ -0,0 +1,10 @@
+// RUN: mlir-opt --test-emulate-narrow-int="memref-load-bitwidth=32" --cse --verify-diagnostics --split-input-file %s
+
+func.func @transfer_read_non_subbyte_element(
+    %arg0: memref<4x?x16xf16>, %arg1: index, %arg2: index, %arg3: index) {
+  %cst = arith.constant 3.000000e+00 : f16
+  // expected-error @below {{failed to legalize operation 'vector.transfer_read' that was explicitly marked illegal}}
+  vector.transfer_read %arg0[%arg1, %arg2, %arg3], %cst :
+    memref<4x?x16xf16>, vector<8xf16>
+  return
+}